Nonhuman primates can serve as acceptable models for studying the activity of physiological systems in humans. The purpose of our research program is to study and determine the type and magnitude of effects several types of drugs can have on physiological activity including heart rate, arterial blood pressure, core body temperature and learned behavior in unanesthetized nonhuman primates. Drugs selected for study are representative of psychomotor stimulants, barbiturates, narcotic analgesics and narcotic antagonists. To obtain direct measurement of blood pressure and the intravenous administration of drugs, squirrel monkeys are surgically prepared with chronically indwelling arterial and venous catheters. Changes in learned behavior in squirrel monkeys and chimpanzees following drug injection are quantitated and provide a measure of the behavioral effects of the drugs. BIBLIOGRAPHIC REFERENCES: Gonzalez, F.A. and Byrd, L.D.: Mathematics underlying the rate-dependency hypothesis. Science 195: 546-550, 1977. Byrd, L.D.: Responding in the squirrel monkey under fixed-ratio schedules of stimulus termination. Journal of the Experimental Analysis of Behavior, 1977 (in press).